Tubular shapes with wavy edges made from rubber or other plastics generally by molding the shape and compressing it when in service to serve as a spring are well known as shown in U.S. Pat. No. 5,141,697 (ribs control buckle locations); U.S. Pat. No. 4,235,427 (bellows wall on plastic tube); U.S. Pat. No. 5,326,083 (elastomer tubular shape for automotive use; U.S. Pat. No. 3,037,764 (elastomer tube with external scores used as a spring); U.S. Pat. No. 5,868,384 (steel tube surrounded by rubber cylinder with both compressed to make a spring with an internal stiffener); U.S. Pat. No. 3,409,284 (molded rubber cylindrical shape used a spring); U.S. Pat. No. 3,315,951 (bellows shaped rubber tube with ribs); U.S. Pat. No. 5,351,844 (elastomer cylindrical shape with metal end plates used as a spring and U.S. Pat. No. 6,250,617 (bellows shaped rubber tube with metal rings at the bellows peaks to hold an outside dimension in a surrounding tube). WO 8901577 shows what appears to be a fabricated metal bellows for a low force application with opposed or offset undulations used as a spring for sensitive instruments that require low hysteresis such as with measuring instruments. It does not appear that the unique shape is made by simple compression and the shape may be fabricated and rolled into a tube. The key seems to be the positioning of the bends with respect to the neutral axis.
U.S. Pat. No. 6,896,049 illustrates a metal cylinder compressed to the point of collapse to use as a seal at the outward buckle locations. U.S. Pat. No. 6,182,755 assigned to Sandia is for a pre-made metallic bellows that is run in under tension and is made to fold downhole under a compressive force until the folds engage a surrounding surface for sealing.
Most of the references described above are compressed cylinders used as springs and made from resilient rubber structures that are molded to have an undulating wall or scored or ribbed to control where and the extent of buckling that occurs under compressive force as a way to control the force delivered by the spring. Clearly many of these are bulky structures not at all suitable for being a component of a downhole tool that needs significant spring force to create some motion in the operational sequence of a downhole tool.
Some of these references use a fabricated bellows or a scored cylinder not for spring use but for sealing.
The present invention has a variety of aspects. The structure in one embodiment can be created downhole when a cylinder assembled to a tool is compressed downhole. The present invention has a rotational locking feature in a spring. It allows taking flow through a spring as a pressure conductor where there is a pressure differential between the inside and the outside of the tube-shaped spring, represented schematically by arrows 29 and 31 to indicate a differential pressure in either direction. Alternatively there can be openings 27 in the wall to act as dampeners as flow represented by arrow 33 passes through them during movement of the spring. Compressing a cylinder between a mandrel on the inside and a cover tube on the outside is another feature of the invention. The use of a cylindrical spring in a metal to metal seal in a packer is an application of the present invention.
Some packers used downhole employ metal to metal sealing technology against large differential pressures and in hostile temperature environments. In such applications a large spring force is required over a long displacement to retain the metal to metal seal and to compensate for anticipated temperature differentials that can also affect the set of the metal to metal seal. A large spring force may be also required to compensate for the axial backlash (slop) inherent in locking devices such as body lock rings or ratchets that occurs when removing the setting force.
Accordingly, the present invention seeks to provide such a structure that will function in this service as well as other high demand spring applications in space limited environments such as those that the art described above are not designed to be used. Those skilled in the art will appreciate that tubular springs of the present invention can retain pressure differentials, transmit torque and can be fixedly retained at the ends to facilitate mill out of the tool in which they are mounted. Such tubular springs can be mounted to an assembled tool as cylinders and compressed into operating shape downhole or they can be deformed prior to assembly and compressed into position in a downhole tool assembly. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings, recognizing that the full scope of the invention is given by the claims.